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docs: fix memory layout comment in instructions sysvar #238

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joncinque merged 2 commits into from
Jul 24, 2025
Merged

docs: fix memory layout comment in instructions sysvar #238

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docs: fix memory layout comment in instructions sysvar
dhl Jul 18, 2025
a56f1e5
rewrite
dhl Jul 24, 2025
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32 changes: 21 additions & 11 deletions instructions-sysvar/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -82,19 +82,29 @@ bitflags! {
}
}

// First encode the number of instructions:
// [0..2 - num_instructions
// Instructions memory layout
//
// Then a table of offsets of where to find them in the data
// 3..2 * num_instructions table of instruction offsets
// Header layout:
// [0..2] num_instructions (u16)
// [2..2 + 2*N] instruction_offsets ([u16; N])
//
// Each instruction is then encoded as:
// 0..2 - num_accounts
// 2 - meta_byte -> (bit 0 signer, bit 1 is_writable)
// 3..35 - pubkey - 32 bytes
// 35..67 - program_id
// 67..69 - data len - u16
// 69..data_len - data
// Each instruction starts at an offset specified in `instruction_offsets`.
// The layout of each instruction is relative to its start offset.
//
// Instruction layout:
// [0..2] num_accounts (u16)
// [2..2 + 33*A] accounts ([AccountMeta; A])
// [2 + 33*A..34 + 33*A] program_id (Pubkey)
// [34 + 33*A..36 + 33*A] data_len (u16)
// [36 + 33*A..] data (&[u8])
//
// AccountMeta layout:
// [0..1] meta (u8: bit 0: is_signer, bit 1: is_writable)
// [1..33] pubkey (Pubkey)
//
// Where:
// - N = num_instructions
// - A = number of accounts in a particular instruction
#[cfg(not(target_os = "solana"))]
#[cfg_attr(feature = "dev-context-only-utils", qualifiers(pub))]
fn serialize_instructions(instructions: &[BorrowedInstruction]) -> Vec<u8> {
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